The present invention relates to an optical deflector for reflecting a ray from a light source and scanning the reflected ray.
Jpn. Pat. Appln. KOKAI Publication No. 62-210418 discloses an example of conventional optical deflectors. FIG. 29 shows the structure of the optical deflector disclosed in this publication. As shown in FIG. 29, this optical deflector is composed of a movable unit 610, supporting springs 614, magnetic yokes 618, and permanent magnets 619. The movable unit 610 is composed of a mirror 611, a mirror holder 612 and driving coils 613.
Rectangular holes 617 are formed in both ends of the mirror holder 612. Inner ends of the magnetic yokes 618 are inserted into the respective holes 617 so as to oppose the whole surface of magnetic poles of the permanent magnets 619. The driving coils 613 are made on the back side of the mirror 611 so as to surround the respective holes 617. Both of the driving coils 613 have the same shape and the same number of windings. The supporting springs 614 are flat, thin plates. Inner ends of the supporting springs 614 are symmetrically fitted to both sides of the movable unit 610 and the other ends (outer ends) are fixed to respective fixing portions 615 with screws 616. The position of the supporting springs 614 in the X direction is at the center of the movable 610.
The following will describe the operation of this optical deflector. When electric currents having the same amperages are applied to the two driving coils 613, a couple of forces around the Y axis is generated at the two driving coils 613 by the currents passing through the driving coils 613 and a magnetic field generated by the permanent magnets 619 and the magnetic yokes 618 near the driving coils 613. This causes the movable unit 610 to be swung around the Y axis. When the mirror 611 of the movable unit 610 which is being swung is irradiated with a ray such as a laser ray, the laser ray or the like ray reflected on the mirror 611 can be scanned.
Jpn. Pat. Appln. KOKAI Publication No. 1-195414 discloses an example of another optical deflector. As shown in FIG. 30A, in this example, a mirror 4, a driving coil 5 and ligaments 3 are formed in a body to constitute a mirror vibrator 10. This vibrator 10 is held by a frame 2. Next, as shown in FIG. 30B, this frame 2 is stuck on an "L"-like member 8 and a block member 9 and then permanent magnets 6 for excitation are fitted thereto, so as to manufacture an optical deflector.
In the case in which the mirror vibrator 10 is fixed onto the "L"-like member 8 and a block member 9 through the frame 2, from the viewpoint of holding the two ligaments 3, which hold and support the mirror 4 and the driving coil 5 therebetween and are weak, the frame in a reversible U-shaped form is essential.
However, the structure disclosed in the Jpn. Pat. Appln. KOKAI Publication No. 62-210418 has a drawback that the rigidity of the movable unit 610 decreases on the basis of the presence of the holes 617 in the movable unit 610, and an unnecessary resonance is liable to be generated in the case in which the deflector is driven by a high frequency.
Specifically, in the magnetic circuit in the prior art the two magnetic yokes 618 are inserted in the movable unit so that the gaps between the respective magnetic yokes 618 and permanent magnets 619 are narrow. Thus, magnetic-flux densities at the driving coils 613 are strong and thus a driving force generated at the movable unit 610 is large. However, the rigidity of the movable unit 610 decreases on the basis of the presence of the holes 617 in the movable unit 610, and an unnecessary resonance is liable to be generated in the case in which the deflector is driven by a high frequency.
Moreover, the holes 617 are made in the movable unit 610, and accordingly the area of the movable unit 610 becomes large. Furthermore, the moment of inertia can become very large since in the movable unit 610 the mirror having large area and thickness is arranged on the mirror supporter 612 having large area and thickness. In the case in which the moment of inertia is large when the movable unit 610 is driven by a high frequency, inconveniently the deflection angle of the movable unit 610 becomes small.
In the structure of the mirror vibrator 10 having at its single side the frame 2, disclosed in the Jpn. Pat. Appln. KOKAI Publication No. 1-195414, the frame 2 is positioned adjacently to the driving coil 5, and thus the distance between the driving coil 5 and the permanent magnet 6 becomes long on account of the intervention of the frame 2. As a result, the magnetic field from the permanent magnet 6, which acts on the driving coil 5, decreases, thereby making its driving force small. Therefore, there arises a drawback that it is difficult to ensure the driving force. To avoid this drawback, it is permissible that the distance between the frame 2 and the driving coil 5 is made longer, and the permanent magnet 6 is located between them. In this case, however, the size of the chip becomes larger because the distance between the frame 2 and the driving coil 5 is longer, and thus manufacturing costs rise.
It can be considered that after the frame 2 is removed, the mirror vibrator 10 is fixed onto the "L"-like member 8 or a block member 9. However, there arise problems that handling is difficult and its characteristic also changes to a great extent.
Therefore, a first object of the present invention is to provide an optical deflector wherein any unnecessary resonance does not arise by improvement in the rigidity of an movable unit even when the deflector is driven by a high frequency and the driving force of the movable unit is made large by a closed magnetic circuit making the magnetic-flux density in its movable coil large to give a large deflection angle at a small electric power consumption.
A second object of the present invention is to provide an optical deflector which is small-sized and highly efficient and can reduce electric power consumption and stabilize its characteristic by connecting at least two elastic members to a movable plate, separating supporters connected to the respective elastic members, and making at least the supporter, the movable plate and the elastic members monolithically formed in a body, and a method for producing the same.